Photomask frame modification to eliminate process induced critical dimension control variation

ABSTRACT

An apparatus comprising a mask having an active device area and a moat. The moat substantially surrounds the mask active device area and has a width greater than a plasma specie diffusional length. A method comprising depositing a layer of resist on a mask substrate having transparent and opaque layers; and exposing the resist layer to radiation. The radiation is patterned to produce features within an active device area. The radiation is also patterned to produce a moat substantially surrounding the active device area having a width greater than a plasma specie diffusional length.

FIELD OF INVENTION

The field of the invention relates to semiconductor manufacturinglithography technology and more specifically to mask features designedto improve critical dimension control.

BACKGROUND OF THE INVENTION

The various conducting lines and other features found within asemiconductor chip are created by lithographic means. That is, light ispassed through a mask and focused onto a semiconductor wafer surfacecoated with a resist. The mask contains opaque and transparent areassuch that, for negative resists, opaque regions correspond to thedesired features formed on the semiconductor wafer surface (such astransistor gates or metal interconnection lines). Alternatively, if apositive resist is used, the transparent regions correspond to thedesired features.

The critical dimension of a semiconductor process is used to refer toone of the process's smallest achievable dimensions. For example, thesmallest feature size formed in a direction parallel to the surface ofthe wafer. Currently, a horizontal critical dimension of leading edgesemiconductor devices is 0.13-0.25 micron (μm). As the projection opticsof today's leading edge exposure tools reduce the optical image from themask by approximately 4:1, the critical dimension of today's leadingedge masks is approximately 0.52-1.0 um (4×0.13-0.25=0.52-1.0).

A problem with masks is the variation of the mask's critical dimensionat the outer edge of a die pattern. That is, as shown in FIG. 1, a mask100 typically has a central area 101 having the various features formedon the semiconductor die. This central area 101 is also referred to as adie pattern, an active area, an active device area or the like. The areaoutside the active device area, referred to as the inactive area 102, islargely unused space. For the most part, the most meaningful features onthe mask are those that help create the features on the silicon chip(which are within the active area 101). Typically, alignment features103 a-d (used for mask alignment purposes) are the main features usedwithin the inactive area 102.

It has been observed that the smallest achievable feature size (i.e., acritical dimension) on the mask increases at the outer edge 104 of theactive area 101. For example, FIG. 2a shows the variation 200 of amask's Final Check Critical Dimension (FCCD) with the mask's radius.Toward the outer edge of the active area 201 (approximately 55000 μmfrom the mask's center in this example) there is a sharp increase in thecritical dimension range from approximately 0.910-0.940 μm to0.950-0.965 μm.

This lack of control usually affects features commonly referred to asmetro cells. Metro cells 202 are a set of features used for thealignment of a lithographic stepper. As metro cells are usually placednear the outer edge of the active area 104 (referring briefly back toFIG. 1), metro cells 202 tend to be more distorted than other features.Thus FIG. 2a shows the critical dimension of the metro cells 202 withinan undesired 0.950-0.965 μm critical dimension range. FIG. 2b shows anSEM photograph of an inner feature edge 203 that is within a mask'sactive device area (101 of FIG. 1) and sufficiently far from the activedevice area edge (104 of FIG. 1). FIG. 2c shows an SEM photograph of ametro cell edge 204 from the same mask as that shown in FIG. 2b. Theloss of critical dimension control is seen by comparison of FIG. 2b withFIG. 2c. The metro cell's edge 204, being substantially more sloped thanthe inner feature edge 203, results in a larger metro cell 202 criticaldimension.

The inability to keep the metro cell's critical dimension within anormal range (e.g., 0.910-0.940μm) results in manufacturinginefficiencies. Specifically, the mask has to be manually or customexposed in order to compensate for the distortion to the metro cell.This custom fitting procedure slows down the manufacturing processresulting in added expense (through wasted time). If the metro cellcritical dimension could be manufactured within the same range as thefeatures within the active area, the custom fitting procedure may beeliminated resulting in substantial savings to current manufacturingcosts.

SUMMARY OF THE INVENTION

An apparatus is described comprising a mask having an active device areaand a moat. The moat substantially surrounds the mask active device areaand has a width greater than a plasma specie diffusional length. Amethod is described comprising depositing a layer of resist on a masksubstrate having transparent and opaque layers; and then exposing theresist layer to radiation. The radiation is patterned to producefeatures within an active device area. The radiation is also patternedto produce a moat substantially surrounding the active device areahaving a width greater than a plasma specie diffusional length.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated by way of example and notlimitation in the figures of the accompanying drawings, in which likereferences indicate similar elements, and in which:

FIG. 1 shows a typical mask.

FIG. 2a shows critical dimension versus mask radius without moatcorrection.

FIG. 2b shows an inner feature edge.

FIG. 2c shows a metro cell edge.

FIG. 3a shows material used to form a mask.

FIG. 3b shows the material of FIG. 3a covered with resist.

FIG. 3c shows the resist of FIG. 3b exposed to radiation.

FIG. 3d shows the resist of FIG. 3c after an etch.

FIG. 3e shows the material of FIG. 3a after an etch.

FIG. 3f shows the material of FIG. 3e after the resist is removed.

FIG. 4 shows a mask having a transparent moat.

FIG. 5 shows an example of critical dimension control as a function ofmoat width.

FIG. 6 shows a mask embodiment having a transparent inactive area.

FIG. 7 shows a mask embodiment having an opaque moat.

FIG. 8a shows a mask covered with resist.

FIG. 8b shows a mask embodiment having a semi-transparent moat.

DETAILED DESCRIPTION

An apparatus is described of a mask having an active device area and amoat. The moat substantially surrounds the mask active device area andhas a width greater than a plasma specie diffusional length. A method isdescribed involving depositing a layer of resist on a mask substratehaving transparent and opaque layers; and then exposing the resist layerto radiation. The radiation is patterned to produce features within anactive device area. The radiation is also patterned to produce a moatsubstantially surrounding the active device area having a width greaterthan a plasma specie diffusional length.

These and other embodiments of the present invention may be realized inaccordance with the following teachings and it should be evident thatvarious modifications and changes may be made in the following teachingswithout departing from the broader spirit and scope of the invention.The specification and drawings are, accordingly, to be regarded in anillustrative rather than restrictive sense and the invention measuredonly in terms of the claims.

In order to address the critical dimension variation at the outerregions of the active area the process of mask making should beunderstood and some theories should be discussed as to why the variationoccurs. FIG. 3 shows the general process of manufacturing a mask. FIG.3a shows the material 301 typically used to form a mask. The material301 is typically a three level multilayer structure, however, otherstructures are possible. The first layer 301 a is a transparent materialusually comprised of quartz. However, other materials such as fusedsilica, fluorinated fused silica and CaF₂ may be used as well.

The second layer 301 b is an opaque material such as chrome (Cr) orother metallic. Other materials may be used for the opaque material suchas CrF, or silicon containing materials such as MoSi, NiSi and TiSi.Dielectric absorbing materials may also be used. Also, an antireflective coating (ARC) 301 c may be placed atop the opaque material301 b. The ARC thickness is typically a quarter wavelength of theexposure radiation used during semiconductor device processing. For UVor deep UV applications (having wavelengths from approximately 1E-7 to1E-8 meters) the thickness of the ARC typically ranges from 300 to 25angstroms (A) The ARC is used to reduce optical flaring. The ARC istypically comprised of CrO_(x)N_(y). However, materials such as CrO, SiNand TiN may also be used.

The CD control approach described in this disclosure is also applicableto manufacturing masks for all the Next Generation Lithography (NGL)techniques, including extreme ultraviolet lithography (EUV), X-raylithography, electron-beam projection and ion projection lithography.The discussion herein may also be used for phase shifting masks. Theappropriate substitution for the substrate and opaque layers may be madeby those skilled in the art.

The general idea is that transparent regions are created by etching awaythe opaque material 301 b (along with the ARC in those embodimentsemploying an ARC) at specific regions where transparent areas aredesired. Similar to semiconductor device manufacturing, mask featuresare formed by a lithographic process. Thus, as shown in FIG. 3b, a layerof resist 302 is first formed over the surface. The resist material maybe a polymeric material such as poly(methyl methacrylate) (PMMA),poly(butene-1-sulfone) (PBS) or the ZEP family of chlorinated polymers.However, other materials such as Chemical Amplified Resists (CAR), amongothers, may be used as well.

After the resist layer 302 is formed, it is exposed to radiation 303such as an electron beam (E-beam) including ebeam projection techniques,ion beam or laser beam as shown in FIG. 3c. The radiation 303 source istypically capable of directly writing the desired features in a customfashion into the resist layer 302. That is, different semiconductorchips typically have unique mask sets having their own unique patternsand features.

For a positive resist 302 (as shown in FIG. 3), typically, the radiationsource 303 causes bond breaking between polymer chains within the resistlayer 302. This makes resist regions exposed to the radiation source 303(e.g., resist regions 307 a,b) easily removed by a subsequent(typically) wet develop process. Alternatively, for negative resists,the radiation source 303 causes bond formation between polymer chainswithin the resist layer making the non-exposed regions easily removed bya subsequent (typically) wet develop process. Thus for positive resists302 “written to” regions 307 a,b are removed after the wet developprocess; while, for negative resists, written to regions 307 a,b remainafter the wet develop process.

For positive resists, after exposing the entire mask surface to a(typically) wet develop process, the resist is removed at the written toregions (e.g., regions 307 a,b) which ultimately exposes the underlyingmask material 301 c as shown in FIG. 3d. If a mask without an ARC layer301 c is used, in regard to the example of FIG. 3, opaque layer 301 bwould be exposed.

A subsequent dry etch (i.e., a plasma based etch such as Reactive IonEtch (RIE) or Magnetic—Enhanced Reactive Ion Etch (MERIE)) is typicallyemployed to remove the opaque layer 301 b (and ARC 301 c) as shown inFIG. 3e which exposes the transparent layer 301 a. During these dry etchprocesses a gas is broken down into smaller reactive radicals (such asFluorine or Chlorine) which adsorb into the exposed surface layer (e.g.,opaque layer 301 b), chemically react with and then remove surface layeratoms. This adsorption, reaction and removal activity is commonlyreferred to as reactive ion etching (RIE). Other techniques, such asmagnetron, inductively coupled plasma, neutral loop discharge, electroncyclotron resonance, helicon, or helical resonator may also be employed.

The completed mask, having transparent regions (e.g., 305 a,b) andopaque regions (e.g., 306 a,b,c) is formed once the resist layer 302 isremoved as shown in FIG. 3f.

Refer back to FIG. 1 which shows a top view of a typical completed mask100 (that is, a mask at the stage corresponding to FIG. 30. Note that,typically, inactive area 102 may correspond to an opaque area, whilealignment features 103 a,b,c,d may correspond to transparent areas. Theactive device area 101, having the complex features associated with asemiconductor chip, typically has many small, complicated opaque andtransparent regions in close proximity together.

There are typically two types of active device areas 101 used forcharacterizing masks: clearfield and darkfield. Clearfields are maskshaving the majority of opaque material removed after processing.Darkfields are masks having the majority of opaque material remaining onthe mask after processing.

Because inactive area 102 may be mostly opaque, the active device area101 is surrounded by a region of (typically) chrome that is not etchedduring the mask manufacturing process. Thus, referring to FIG. 1 andFIG. 3, the inactive area 102 may have a layer of resist 302 over itthrough most of the manufacturing process before the final etch step ofFIG. 3f. A theory that correlates the loss of critical dimension controlat the die area edge (e.g., as shown in FIG. 2a) with the presence oflarge amounts of resist 302 in the area surrounding the active devicearea 101 concerns resist loading.

Resist loading is the local dependence of etch rates on resistpatterning density. Possibly, referring back to FIGS. 3e and 3 f, CDcontrol may be a function of the etching of the resist layer 302. Forexample, the resist layer 302 may consume plasma species which affectsCD control.

As such, the amount of resist 302 that is available to consume plasmaspecies within and proximate to a local region is a factor in the etchrates that occur at that local region. Local regions having more resistwill have slower resist etching rates since relatively more plasmaspecies are consumed. Referring to FIG. 1, modulating the amount ofavailable resist within and/or proximate to the active device area edges104 may therefore be employed to control the etching activity near theactive device area edges 104 and prevent the aforementioned CDvariation. One solution to the problem involves introducing some form oftransparency to the inactive area 102 in the completed mask in order toreduce the amount of resist.

This may be accomplished by designing into the mask a pattern thatcorresponds to an area of exposed opaque layer material 301 b in theinactive region 102 during the opaque layer etch step. This exposed areaof opaque layer material corresponds to a transparent region in theinactive region 102 after the mask manufacturing process is completed.The formation of a transparent region results in a moat-like structure(hence the name given to this structure, the moat) that surrounds theactive device area 101.

An embodiment of such a mask design is shown in FIG. 4. FIG. 4 shows anactive device area 401, opaque alignment frame 402, a transparent moat403 and the remaining inactive region 404. Again, this particularembodiment addresses a positive resist mask making process.

The opaque alignment frame 402 is used to align the optical exposuretool during the manufacture of the semiconductor device. Since theopaque alignment frame 402 introduces undesired resist at the activedevice area 401 edge, the opaque alignment frame width 410 should bereduced to a minimal width needed to properly align the manufacturingequipment. Wider widths are acceptable, however, provided criticaldimension control is maintained.

Opaque alignment frame width 410 may also vary according to the variousequipment intended to be used with the mask (if the various equipmenthave different minimum frame width 410 tolerances). The opaque framewidth 410 is also typically uniform around the active device area 401edge. However, different equipment may deviate from a uniform framewidth in order to maximize alignment accuracy.

The embodiment of FIG. 4 shows the opaque alignment frame 402immediately surrounding the active device area 401. However, otherembodiments depending on the equipment employed may insert the opaquealignment frame 402 within the transparent moat 403 as well. This may bedesirable since it removes the resist layer material further away fromthe active device area 401 edge. Again, the amount of distance dependsupon the specific alignment frame requirements and/or alignmentcapabilities of the particular equipment using the mask.

The dimensions of the moat 403 are discussed next. In this embodiment,the moat 403 is transparent in the completed mask. Thus moat 403corresponds to a region of exposed opaque material during the opaquematerial etch step. The moat width 411 is generally a function of twoconstraints: plasma specie diffusional length and mask manufacturingtolerances. By keeping the resist layer material to an inactive region404 placed beyond a plasma specie diffusion length, its effect on theplasma specie density near the active device area 401 edges should beminimized. This sets a lower bound on the moat width.

Plasma based etches (such as RIE based etches) involve a complicatedcombination of various product species, intermediate species andreactant species within the plasma. To first order, the diffusion lengthof a specie is closely related to the specie's mean free path. Thus, forone chrome etch embodiment having 50 mTorr pressure and 25 C.temperature, the mean free path for an oxygen radical is 9.5 mm, whilefor a chlorine radical it is 3.5 mm, according to the followingequation: $\begin{matrix}{\lambda = \frac{1}{\sqrt{2}\pi \quad d_{o}^{2}n}} & \text{Eqn.~~1}\end{matrix}$

In Equation 1, d_(o) is the effective diameter of the specie (such as0.120 nm for an oxygen radical) and n is the density. The density isdictated by the process temperature and pressure. The specie dictatesthe cross-section for collisional interactions and is related to theeffective diameter.

As mentioned above, plasma based etches (such as RIE based etches)involve a complicated combination of various product species,intermediate species and reactant species within the plasma. Highdensity plasmas, as is known in the art, have higher concentrations ofspecies within the plasma. The various species are single atoms andmolecules formed with atoms from elements such as Oxygen (O), Chlorine(Cl), Flourine (F) and Hydrogen (H). These molecules and single atomsmay be ionic or electrostatically neutral.

The elements listed above are a list of typical elements found withinplasmas. However, it is important to note that typical plasmas haveother atoms (such as Chromium (Cr)) in lieu of or in combination with O,Cl, F and H. The presence of these other elements increases thecomplexity (i.e., number of possible specie combinations) within theplasma since they typically can form molecules with O, Cl, F and H aloneor with various combinations of O, Cl, F and H. For example, differentmolecules based upon CrO, CrCl, or CrO₂Cl₂ are all possible within aplasma.

Furthermore, many of the above elements may exist within the plasma bythemselves as a single atom (such as an H atom) or as a molecule such asO₂ or Cl₂. Again, these may be ionic or electrostaticaly neutral. Thus,the number of possible molecules or single atoms within a plasma thatstem from each of the elements present in the plasma is very large.

Each type of molecule or single atom within a plasma corresponds to aspecie within the plasma. Since the minimum bound of the moat width 411is related to plasma specie diffusional length and without fullknowledge of all the reactant species that exist in the plasma used toetch our mask (as is typical in the art), we have relied on empiricaldata to determine moat width 411.

Based on our empirical data, we have found that for a 50 mT plasma, amoat width of 10 mm was sufficient to deliver the desired CD improvementon a clearfield mask. As our plasma contains oxygen (which by itself hasa reactant length of 9.5 mm as discussed above), note that our moatwidth 411 is comparable to the diffusional length of oxygen.

It is therefore possible that oxygen or oxygen based molecules are adominant specie within our plasma and/or represent the specie(s) havingthe longest diffusional length. Dominant species are those species whosedensity within a plasma are most affected by resist loading. Forexample, dominant species may be those species that favor reactions withthe resist as compared to other species. The presence of resist lowersthe proximate density of oxygen.

Thus, moving the moat width 411 beyond the one or more dominant species'diffusional length(s) should noticeably reduce CD variation. Sinceoxygen reacts heavily with available resists, we believe that oxygenand/or molecules based upon oxygen may be a dominant species within ourplasma.

An alternate theory concerns the fact that oxygen may have one of thelonger diffusional lengths of the specie types. For example, recall thatoxygen's diffusional length (9.5 mm) is nearly three times thediffusional length of a monotonic chlorine specie (3.5 mm). Our moatwidth of 10.0 mm may therefore represent a distance greater than thespecie having the longest diffusional length. Alternatively, combiningthe two above perspectives, oxygen may represent the longest, dominantspecie within our plasma. Thus, in such a case, our moat width 411 of10.0 mm is greater than the longest, dominant specie within our plasma.

The 10.0 mm moat width 411 of our embodiment may also represent aweighted diffusional length of the entire plasma. For example, if thediffusional length of each specie (where each diffusional length has acoefficient related to the dominance of its corresponding specie) issummed over all the species within the plasma, an effective diffusionallength of the entire plasma is produced. Given oxygen's strong reactionwith available resists, we would anticipate the oxygen term(s) todominate such an effective diffusional length expression.

The above discussion has related to the minimum bound on the moat width411. The following discussion relates to the maximum bound on the moatwidth 411. FIG. 5 shows the observed relationship between the variationin metro cell critical dimension, normalized to a reference value, as afunction of the normalized moat width 411. Since critical dimensionvariation drops with increasing moat width, the transparent moat width411 could in principle extend (ultimately) to the mask edge 412 itself.Such an approach is shown in FIG. 6. FIG. 6 shows an active device area601 surrounded by an alignment frame 602. The inactive area 604 istransparent.

In many applications, the maximum distance of the moat width 411 may beconstrained by manufacturing issues. There are generally threeconstraints that limit the maximum extent of the moat width 411. Firstof all, there are features in the inactive area, such as alignment marks420 a-d, that should typically not be covered by the moat 403. Second, alarger moat width 411 increases the amount of opaque layer to clearduring the etch step, leading to a longer required etch time and moreresist loss than necessary. Greater resist loss generally degrades etchprofiles, CD range and OPC fidelity. Finally, the radiation exposureprocess is typically a slow, cumbersome and expensive step in maskmanufacturing. Thus, in order to fabricate cost effective masks, theamount of exposure area used to create the moat 403 should be reducedwhere possible.

Thus one may use: 1) Equation 1 in light of a plasma specie's expecteddiffusional lengths and/or dominance, consistent with one or more of thetheories discussed above; and 2) an empirical approach (e.g., varyingmoat widths about values calculated above) to obtain an optimum moatwidth 411.

The embodiment discussed so far has related to a positive resist maskmaking processes. In positive resist processes, the regions of resistthat are written to are removed. Other embodiments relate to negativeresist mask making processes in which the regions of written to resistremain. This alters the previously mentioned cost effectivenessconstraints. For negative resists, the layout of FIG. 6 is most costeffective since no writing is required in the inactive area 604. This isbecause if the inactive area 604 is not written to, all the resist ininactive area 604 is removed. This leaves inactive area 604 as a regionof exposed opaque layer material during the opaque layer etch. Howeverthe other moat width constraints still apply. For example, the inactivearea mask features (e.g., alignment features similar to those in FIG. 4,420 a-d not shown in FIG. 7) should be written to in the negativeresist.

In addition, if the benefits of resist loading reduction are outweighedby the impact to the etch(e.g., the time to etch away the opaque layeris too long, leading to excessive resist loss), some areas of thenegative resist must be exposed to the radiation source to reduce thearea of opaque layer to be etched.

FIG. 7 shows such an approach. In FIG. 7, moat region 703 was exposed tothe radiation source. Since a negative resist is employed, the moatregion 703 remains covered with resist after the resist removal step(e.g. step 3C to 3D in FIG. 3). This leaves region 704 as exposed opaquelayer material during the opaque layer etch step. Region 704 istransparent when the mask is completed, while moat region 703 is opaque.

A tradeoff that arises with negative resist is exposure time vs. amountof opaque layer to etch at the mask periphery. It is more economical toexpose away from the mask edge and closer to the active area. On theother hand, this opaque moat scheme potentially forces a tradeoffbetween resist loading and resist loss.

Other moat embodiments utilize semi-transparent moat regions.Semi-transparent moat regions attempt to modulate the etch rates at theactive device area periphery by forming a micropatterned layer of resistresulting in a semi-transparent moat region.

In FIG. 8a, the mask is covered with resist at the inactive area 803 a,804 a. The mask is written to within a moat region 803 a by theradiation source. However, the radiation source is configured such thatonly some of the resist within region 803 a is written to. Thus, thereexist regions of non-written to resist within regions 803 a. After theresist etch step (e.g. from FIGS. 3C to 3D in FIG. 3), the region 803 awill have a porous layer of resist. This corresponds to a micropatternedregion of exposed opaque material which is used to consume reactantsduring the opaque layer removal step. Thus, as shown in FIG. 8b, whenthe mask is completed, the active device area 801 b is surrounded by asemi-transparent moat region 803 b having regions of opaque materialmixed with transparent material at a subresolution scale. Note thatdistinctions between positive and negative resist are immaterial sinceeither type of resist is partially written to.

What is claimed is:
 1. A mask, comprising: an active device area; and amoat, said moat surrounding said active device area, said moat having awidth, said width tailored to be greater than a diffusional length of aspecie within a plasma, said plasma having been used to etch a portionof an opaque layer of said mask.
 2. The mask of claim 1 wherein saidmoat is transparent.
 3. The mask of claim 1 wherein said specie favors areaction with a resist layer as compared to other species within saidplasma, said resist layer having been formed on said mask to protect nonetched regions of said mask from said plasma during said etch.
 4. Themask of claim 1 wherein said diffusional length is the longestdiffusional length of those species within said plasma that react with aresist layer, said resist layer having been formed on said mask toprotect non etched regions of said mask from said plasma during saidetch.
 5. The mask of claim 1 wherein said diffusional length is aneffective diffusional length for a plurality of species within saidplasma that react with a resist layer, said resist layer having beenformed on said mask to protect non etched regions of said mask from saidplasma during said etch.
 6. The mask of claim 1 further comprising anopaque inactive area surrounding said moat.
 7. The mask of claim 1wherein said active device area comprises transparent regions and opaqueregions.
 8. The mask of claim 7 wherein said opaque regions furthercomprise an anti reflective layer.
 9. The mask of claim 1 wherein saidmoat is opaque.
 10. The mask of claim 1 wherein said moat issemi-transparent.
 11. A mask, comprising: a transparent layer thatallows light to pass through said mask; an opaque layer that thwarts thepassing of light through said mask; a range of metro cell edge slopesthat help form a plurality of metro cells; an active device area, saidactive device area having a range of feature edge slopes, said pluralityof metro cells used to help align said active device area within aphotolithographic tool that exposes a wafer to at least a portion ofsaid light that is allowed to pass through said mask; and a moat regionoutside said active device area, said moat region having a width, saidwidth tailored to be greater than a diffusional length of a speciewithin a plasma, said plasma having been used to etch a portion of saidopaque layer, said range of metro coil edge slopes at or within saidrange of feature edge slopes.
 12. The mask of claim 11 wherein materialfrom said opaque layer is removed from said moat region.
 13. The mask ofclaim 11 wherein said specie favors reaction with a resist layer used toprotect a second portion of said opaque layer from said etch as comparedto other species within said plasma.
 14. The mask of claim 11 whereinsaid diffusional length is the longest diffusional length of thosespecies within said plasma that react with a resist layer used toprotect a second portion of said opaque layer from said etch.
 15. Themask of claim 11 wherein said diffusional length is an effectivediffusional length for a plurality of species within said plasma thatreact with a resist layer used to protect a second portion of saidopaque layer from said etch.
 16. The mask of claim 11 further comprisingan opaque inactive area surrounding said moat region.
 17. The mask ofclaim 11 wherein said active device area comprises transparent regionsand opaque regions.
 18. The mask of claim 17 wherein said opaque regionsfurther comprise an anti reflective layer.
 19. The mask of claim 11wherein material from said opaque layer remains within said moat region.20. The mask of claim 11 wherein said moat region is semi-transparent.21. A method, comprising: forming a layer of resist on a mask substrate,said mask substrate having a transparent layer and an opaque layer; andexposing said layer of resist to radiation, said radiation tailored toproduce features within an active device area, said radiation tailoredto produce a moat surrounding said active device area, said moat havinga width, said width greater than a diffusional length of a specie withina plasma, said plasma to be used to etch a portion of said opaque layer.22. The method of claim 21 wherein said etch further comprises etchingsaid resist layer and said opaque layer such that said moat is atransparent moat.
 23. The method of claim 22 wherein said etch furthercomprises a reactive neutral etch.
 24. The method of claim 22 whereinsaid etch further comprises a reactive ion etch.
 25. The method of claim24 wherein said etch further comprises a magnetic enhanced reactive ionetch.
 26. The method of claim 21 wherein said opague layer furthercomprises a metallic layer.
 27. The method of claim 26 wherein saidmetallic layer further comprises chrome.
 28. The method of claim 21wherein said layer further comprises a silicon containing material. 29.The method of claim 21 wherein said layer further comprises a dielectricabsorbing material.
 30. The method of claim 21 wherein said opaque layerfurther comprises an anti reflective coating.
 31. The method of claim 21wherein said radiation further patterns an alignment frame.
 32. Themethod of claim 21 wherein said radiation is in the form of an E-beam.33. The method of claim 21 wherein said radiation is in the form of alaser beam.
 34. The method of claim 21 wherein said radiation is in theform of an ion beam.
 35. The method of claim 21 further comprisesetching said resist and said opaque layer outside said active devicearea and said moat in order to form an opaque moat.
 36. The method ofclaim 21 further comprising etching said resist and said opaque layersuch that said moat is a semi-transparent moat.
 37. The method of claim21 wherein said plasma is a high density plasma.
 38. A method,comprising: a) transmitting light through a mask, a first portion ofsaid light passing through said mask outside an active device arealocated on said mask such that a moat of light is formed just as saidlight passes through said mask, said moat of light having a widthgreater than a diffusional length of a specie within a plasma, saidplasma having been used to etch an opaque layer of said mask; b)focusing a second portion of said light that has passed through saidactive device area onto a semiconductor wafer that has been coated withresist.
 39. A mask, comprising: a transparent layer that allows light topass through said mask; an opaque layer that thwarts the passing oflight through said mask; a range of metro cell edge slopes that helpform a plurality of metro cells; an active device area, said activedevice area having a range of feature edge slopes, said plurality ofmetro cells used to help align said active device area within aphotolithographic tool that exposes a wafer to at least a portion ofsaid light that is allowed to pass through said mask; and a regionoutside said active device area, said range of metro cell edge slopes ator within said range of feature edge slopes at least in part becausesaid region sufficiently detered etch rate reduction of a plasma etchused to form said metro cell edge slopes, said etch rate reductioncaused by reactions between said plasma and a resist layer that existedon said mask outside said active device area during said plasma etch,said region exposing said opaque layer to said plasma during said plasmaetch.
 40. The mask of claim 39 wherein said resist layer was a negativeresist layer.
 41. The mask of claim 39 wherein said resist layer was apositive resist layer.
 42. The mask of claim 39 wherein said region is atransparent moat that surrounds said active device area, said moathaving a width, said width tailored to be greater than a diffusionallength of a specie, said specie with said plasma.
 43. The mask of claim42 wherein said specie favors a reaction with said resist layer ascompared to other species within said plasma.
 44. The mask of claim 42wherein said diffusional length is the longest diffusional length ofthose species within said plasma that react with said resist layer. 45.The mask of claim 42 wherein said diffusional length is an effectivediffusional length for a plurality of species within said plasma thatreact with said resist layer.
 46. The mask of claim 39 wherein saidregion is a transparent region that surrounds said active device area.47. The mask of claim 39 wherein said region is a transparent regionthat surrounds an opaque moat, said opaque moat surrounding said activedevice area.
 48. The mask of claim 39 wherein said region is asemi-transparent moat that surrounds said active device area.
 49. Amethod, said method comprising: forming a layer of resist on a masksubstrate, said mask substrate having a transparent layer and an opaquelayer; and exposing said layer of resist to radiation, said radiationtailored to produce: 1) features within an active device area, 2) metrocells outside said active device area, and 3) a region outside saidactive device area; developing said resist so that said resist isremoved from said region wherein, said range of metro cell edge slopesare at or within said range of feature edge slopes at least in partbecause said region sufficiently detered etch rate reduction of a plasmaetch used to form said metro cell edge slopes, said etch rate reductioncaused by reactions between said plasma and a resist layer that existedon said mask outside said active device area during said plasma etch,said region exposing said opaque layer to said plasma during said plasmaetch.